Servo control device with a function for automatically regulating a control system with autonomous stabilization

Abstract

Servo control device for a machine tool with a feed spindle driven by a servo motor, comprising: a speed command generation device (1) to generate a speed command value for the servo motor; a torque command generation unit (2) to generate a torque command value for the servo motor; a speed detection unit (3) to detect the speed of the servo motor; a speed control loop (4) comprising the speed command generation unit, the torque command generation unit, and the speed detection unit; a speed control gain adjustment unit (5) to adjust a speed control gain, which is a control gain for the speed control loop; a unit (6) for inputting a sinusoidal disturbance in order to perform a sinusoidal excitation on the speed control loop; a frequency property calculation unit (7) to estimate the gains and phases of speed control loop input and output signals from the speed control loop outputs when a sine wave is input into the speed control loop, and a gain control unit (8) to regulate the speed control gain online, wherein the velocity control gain is reduced and the sinusoidal excitation is temporarily stopped if the velocity control loop (4) has entered an oscillatory state and become unstable due to an increased velocity control gain, and the sinusoidal excitation is restarted after the velocity control loop (4) has been stabilized using a velocity control gain that is lower than in the unstable state.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a servo control device, and more particularly to a servo control device having the function of automatically regulating a control system with autonomous stabilization. 2. Description of the state of the art

[0002] Many devices and methods related to measuring the frequency characteristics of servo control systems have been proposed and are widely used in measuring the transmission characteristics of machine tool feed screws. Methods for automatically adjusting control gains are also known.

[0003] A gain control method in which a sinusoidal excitation wave is applied as a disturbance to a control system of a servo control device is known (for example, republication of PCT International Application No. WO 2009 / 19953, hereinafter referred to as “Patent Document 1”). Fig. 1 shows a block diagram of a conventional engine control device. In Fig. 1, a motor control device 1000 includes a motor 1001, a detection unit 1002, a control unit 1003, a machine 1004, a disturbance signal generation unit 1005, a compensation driving force detection unit 1006, a vibration calculation unit 1007, a vibration detection unit 1008, a vibration storage unit 1009, and an open-loop simulation gain calculation unit 1010. Patent Document 1 discloses that the disturbance signal generation unit 1005 adds a sinusoidal excitation wave as a disturbance signal to a driving force output from the control unit 1003.

[0004] However, the conventional technology has the problem that the engine control device cannot recover automatically when the engine control device enters an unstable state during online automatic regulation of the control system.

[0005] EP 2 980 986 A1 discloses a motor control device in which a maximum value for a stiffness index is automatically adjusted. EP 2 178 202 A1 shows a motor control device that detects a vibration state of a feedback loop and adjusts a gain value accordingly. US 2002 / 0 022 903 A1 relates to automatic calibration of a motor control system, and EP 2 077 614 A2 relates to a servo control device in which the frequency of a disturbance is analyzed with a specific phase shift. SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a servo control apparatus which, when a control system has become unstable, can perform a control sequence for online automatic control of the control system to completion while automatically stabilizing the control system.

[0007] A servo control device according to one embodiment of the present invention is a servo control device for a machine tool having a feed screw driven by a servo motor. The servo control device includes a speed command generation unit for generating a speed command value for the servo motor; a torque command generation unit for generating a torque command value for the servo motor; a speed detection unit for detecting the speed of the servo motor; a speed control loop including the speed command generation unit, the torque command generation unit, and the speed detection unit; a speed control gain setting unit for setting a speed control gain, which is a control gain for the speed control loop;a unit for inputting a sinusoidal disturbance to provide a sinusoidal excitation to the speed control loop;a frequency characteristic calculation unit for estimating the gains and phases of speed control loop input and output signals from the outputs of the speed control loop when a sine wave is input to the speed control loop, and a gain adjustment unit for adjusting the speed control gain online. When the speed control loop has entered an oscillation state and become unstable due to an increased speed control gain, the speed control gain is reduced and the sine excitation is temporarily stopped, and the sine excitation is restarted after the speed control loop has stabilized using a speed control gain lower than that in the unstable state. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The objects, features and advantages of the present invention will become more apparent from the following description of an embodiment taken in conjunction with the accompanying drawings, in which Fig. 1 is a block diagram showing the structure of a conventional servo control device; Fig. 2 is a block diagram showing the structure of a servo control device according to an embodiment of the present invention; and Fig. 3 is a flowchart of the operation of the servo control apparatus according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Referring to the drawings, a servo control apparatus according to an embodiment of the present invention will be described below. Fig. Figure 2 is a block diagram showing the structure of the servo control device according to the embodiment of the present invention. A servo control device 101 according to the embodiment of the present invention is a servo control device for a machine tool having a feed screw driven by a servo motor 20. The servo control device 101 includes a speed command generation unit 1, a torque command generation unit 2, a speed detection unit 3, a speed control loop 4, a speed control gain adjustment unit 5, a sinusoidal disturbance input unit 6, a frequency characteristic calculation unit 7, and a gain adjustment unit 8.In the servo control device 101 of the embodiment of the present invention, when the speed control loop 4 has fallen into an unstable oscillation state due to an increase in the speed control gain, the speed control gain is reduced, and sinusoidal excitation is temporarily stopped. After the speed control loop 4 stabilizes using a speed control gain lower than that in the unstable state, sinusoidal excitation is restarted. As a method for reducing the speed control gain, for example, the speed control gain can be changed to a minimum value within a certain gain tolerance or phase tolerance.

[0010] The speed command generation unit 1 generates a speed command value for the servo motor 20. The speed command value generated by the speed command generation unit 1 is output to an adder 10. The adder 1 adds a sinusoidal disturbance input by the sinusoidal disturbance input unit 6 to the speed command value and subtracts therefrom a speed detection value detected by the speed detection unit 3. The adder 10 outputs a calculation result to the speed control gain adjustment unit 5.

[0011] The torque command generation unit 2 generates a torque command for the servo motor 20. More specifically, the torque command generation unit 2 calculates the product of the calculation result of the adder 10 and a speed control gain and outputs a torque command value for driving the servo motor 20. The servo motor 20 drives a driver (not shown) through a transmission mechanism 30.

[0012] The speed detection unit 3 detects the speed of the servo motor 20. The speed of the servo motor 20 is detected, for example, using an encoder provided in the servo motor 20, but the invention is not limited thereto.

[0013] The speed control loop 4 includes the speed command generation unit 1, the torque command generation unit 2, and the speed detection unit 3. The speed control gain setting unit 5 sets a speed control gain regulated by the gain regulation unit 8 with respect to the calculation result calculated by the adder 10 of subtracting the speed detection value detected by the speed detection unit 3 from the sum of the sinusoidal disturbance introduced by the sinusoidal disturbance input unit and the speed command value.

[0014] The sinusoidal disturbance input unit 6 applies a sinusoidal excitation to the speed control loop 4. More specifically, the sinusoidal disturbance input unit inputs a sinusoidal disturbance to the adder 10.

[0015] The frequency characteristic calculation unit 7 estimates the gains and phases of speed control loop input and output signals from outputs of the speed control loop 4 when a sine wave is input to the speed control loop 4. The frequency characteristic calculation unit 7 expresses an output of the speed control loop 4 as a Fourier series with any number of terms, using a disturbance input frequency from the sinusoidal disturbance input unit 6 as the base frequency, and calculates the amplitude and phase of a base component of the Fourier series to calculate the frequency characteristics online. The gain adjustment unit 8 preferably determines the adjustment amount of a speed control gain based on the difference between a desired target evaluation function value and an evaluation function value by an actual excitation.

[0016] When the speed control loop 4 has entered an oscillation state and become unstable due to an increased speed control gain, the servo control device 101 reduces the speed control gain and temporarily stops the sinusoidal excitation. After that, the servo control device 101 stabilizes the speed control loop 4 using a speed control gain lower than that in the unstable state and then restarts the sinusoidal excitation. When the control system has become unstable during online automatic regulation, the servo control device according to the embodiment of the present invention temporarily and significantly reduces a control gain as described above to stabilize the control system. Therefore, it is possible, in principle, to complete a regulation sequence.Furthermore, the servo control device immediately and temporarily stops and restarts a sequence when a large oscillation has occurred, allowing safe and automatic regulation even if an operator does not notice the instability.

[0017] Next, referring to the flowchart of Fig. 3, the operation of the servo control device according to the embodiment of the present invention will be described. In step S101, the sinusoidal disturbance input unit 6 initializes an input frequency. In step S102, the sinusoidal disturbance input unit 6 updates the input frequency. In step S103, the sinusoidal disturbance input unit 6 inputs a sinusoidal disturbance to the speed control loop 101.

[0018] Next, in step S104, the speed detection unit 3 detects the speed of the servo motor 20. In step S105, the torque command generation unit 2 generates a torque command from a speed command value, the speed detection value, and a speed control gain.

[0019] Next, in step S106, it is determined whether or not the gain control unit 8 has detected instability of the speed control loop 4. Specifically, the gain control unit 8 determines that the speed control loop 4 has become unstable when the speed control loop 4 has entered an oscillation state due to the increased speed control gain.

[0020] If the gain control unit 8 determines instability of the speed control loop 4 in step S106, the gain control unit 8 reduces the speed control gain within a permissible range in step S107. As a method for reducing the speed control gain within a permissible range, the speed control gain can be changed, for example, to a permissible minimum value.

[0021] Next, in step S108, the sinusoidal disturbance input unit 6 stops the sinusoidal excitation. In other words, the sinusoidal disturbance input unit 6 stops the input of the sinusoidal disturbance to the speed control loop 4. In step S109, the gain control unit 8 temporarily stops the measurement of the frequency characteristics for gain control.

[0022] In step S110, after a sufficient time has elapsed, the gain control unit 8 restarts measuring the frequency characteristics. Next, in step S111, the gain control unit 8 adjusts the speed control gain. In other words, after stabilization, the sinusoidal excitation is restarted using a lower speed control gain than in the unstable state. Afterward, the operation returns to step S101, and steps S101 to S106 are performed again.

[0023] On the other hand, if the gain control unit 8 does not detect instability of the speed control loop 4 in step S106, the frequency characteristic calculation unit 7 calculates the frequency characteristics at the determined frequency in step S112.

[0024] Next, the sinusoidal disturbance input unit 6 determines whether or not the input frequency of the sinusoidal disturbance has reached a peak value in step S113.

[0025] When the sinusoidal disturbance input unit 6 determines in step S113 that the input frequency of the sinusoidal disturbance has reached the maximum value, the operation returns to step S101 and steps S101 to S113 are performed again.

[0026] On the other hand, if the sinusoidal disturbance input unit 6 does not determine that the sinusoidal disturbance input frequency has reached the maximum value in step S113, the gain adjustment unit 8 adjusts the speed control gain in step S114.

[0027] Next, in step S115, the gain control unit 8 determines whether the speed control gain has reached a stable state or not.

[0028] If the gain control unit 8 determines in step S115 that the speed control gain has reached a stable state, the sequential operation is terminated. On the other hand, if the gain control unit 8 does not determine in step S115 that the speed control gain has reached a stable state, the operation returns to step S101, and steps S101 to S115 are performed again.

[0029] As described above, when the speed control loop 4 has become unstable, the servo control device 101 changes the speed control gain and performs the sine excitation in a repeated manner until the speed control loop 4 is stabilized, and starts measuring the frequency characteristics of the speed control loop 4 again after the speed control loop 4 is stabilized.

[0030] As described above, according to the servo control apparatus of the embodiment of the present invention, when the control system has become unstable during the online automatic regulation, the control gain is temporarily and significantly reduced to stabilize the control system.

[0031] According to the servo control device of the embodiment of the present invention, when the control system has become unstable, it is possible to perform the control sequence for the online automatic control of the control system to completion while automatically stabilizing the control system.

Claims

[1] Servo control device for a machine tool with a feed screw driven by a servo motor, comprising: a speed command generating device (1) for generating a speed command value for the servo motor; a torque command generating unit (2) for generating a torque command value for the servo motor; a speed detection unit (3) for detecting the speed of the servo motor; a speed control loop (4) comprising the speed command generation unit, the torque command generation unit, and the speed detection unit; a speed control gain setting unit (5) for setting a speed control gain which is a control gain for the speed control loop; a unit (6) for inputting a sinusoidal disturbance to provide a sinusoidal excitation to the speed control loop; a frequency characteristic calculation unit (7) for estimating the gains and phases of speed control loop input and output signals from the outputs of the speed control loop when a sine wave is input to the speed control loop, and a gain control unit (8) for regulating the speed control gain online, wherein the speed control gain is reduced and the sinusoidal excitation is temporarily stopped when the speed control loop (4) has fallen into an oscillation state and become unstable due to an increased speed control gain, and the sinusoidal excitation is restarted after the speed control loop (4) has been stabilized using a speed control gain that is lower than in the unstable state. [2] A servo control device according to claim 1, wherein the speed control gain is changed and the sinusoidal excitation is performed in a repeated manner until the speed control loop (4) is stabilized when the speed control loop (4) has become unstable, and after the stabilization of the speed control loop (4), the measurement of the frequency characteristics of the speed control loop (4) is started again.

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